2.5 - Rotation Orders for Bones [Durian Rigging Request]

This commit is the start of an implementation of (euler) rotation orders for Bones (later to be extended to Objects too). 

Technical details and references can be found at:
http://wiki.blender.org/index.php/User:Aligorith/EulerRotationOrder

In short, I've added a new set of Euler conversion functions (EulO... and ...EulO), coexisting with the old functions for now, which can handle different rotation orders.

Changes have only been made to the basic evaluation code. However, the following places will still need modifications:
* Transform code - needs to be made to use functions which take rotation order into account instead of using XYZ only
* Rotation constraints - same story
* Other rotation editing tools for armatures also need a check up, since there might have been some missing code when I ported eulers earlier

source/blender/editors/transform/transform.c

@@ -2670,7 +2670,7 @@ static void ElementRotation(TransInfo *t, TransData *td, float mat[3][3], short
 				/* this function works on end result */
 				protectedQuaternionBits(td->protectflag, td->ext->quat, td->ext->iquat);
 			}
-			else {
+			else { // TODO: need some methods for the new euler types...
 				float eulmat[3][3];
 
 				Mat3MulMat3(totmat, mat, td->mtx);